Multi-piece circumferential retaining ring

ABSTRACT

Embodiments of retaining rings for use in orthopedic implants, for example, are disclosed. Such embodiments may include two or more pieces that are assembled so that the pieces overlap each other and define an inner diameter that is less than the diameter of a part to be retained. In particular embodiments, the assembled pieces define a complete circle, and they may be substantially planar or include bends, waves or other geometric configurations.

The present disclosure relates to devices and implants used inosteosynthesis and other orthopedic surgical procedures. Specifically,the present disclosure contemplates a multi-piece retaining structurefor use with orthopedic implants or other devices.

Several techniques and systems have been developed for correcting andstabilizing damage or malformation of bones, especially the long bonesand the spine. In some of these systems, components can be preliminarilylinked together, then adjusted with respect to each other and finallylocked together. For example, in multi-axial anchor devices, a receivermember and an anchor member (e.g. a screw) may be connected so that thehead of the anchor is in the receiver member, and the anchor ismulti-axially pivotable with respect to the receiver member. The anchormember must be held or retained against falling out of or through thereceiver member, yet must be pivotable until locked. Other types oforthopedic implants have parts that must be held with respect to eachother.

Clamps, caps and other devices have been proposed to accomplish suchrelative holding or retaining. Frequently, however, such devices arerelatively bulky and/or provide a relatively high profile on anorthopedic implant or system. Such a high profile can interfere withother parts of an orthopedic implant, or can interfere with or causedamage to tissues adjacent the implant or implant system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an embodiment of retainingapparatus.

FIG. 2 is a perspective view of the embodiment illustrated in FIG. 1.

FIG. 3 is a side elevational view of a part of the embodimentillustrated in FIG. 1.

FIG. 4 is a top plan view of the part illustrated in FIG. 3.

FIG. 5 is a perspective view of an embodiment of an orthopedic implantwith which the embodiment of FIG. 1 can be used.

FIG. 6 is a partial cut-away view in perspective of the embodimentillustrated in FIG. 5, with an elongated member.

FIG. 7 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 8 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 7.

FIG. 9 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 10 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 11 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 10.

FIG. 12 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 13 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 12.

FIG. 14 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 15 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 14.

FIG. 16 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 17 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 16.

FIG. 18 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 19 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 18.

FIG. 20 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 21 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 20.

FIG. 22 is a perspective view of an embodiment of part of a retainingapparatus.

FIG. 23 is a perspective view of a retaining apparatus incorporating theembodiment illustrated in FIG. 20.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theclaims is thereby intended, such alterations and further modificationsin the illustrated device, and such further applications of theprinciples of the disclosure as illustrated therein, being contemplatedas would normally occur to one skilled in the art to which thedisclosure relates.

Referring generally to FIGS. 1-6, there is shown an embodiment of aretainer 30. Retainer 30 can be used along with a variety of orthopedicimplants or other devices that require connection of one part withanother, as further discussed below. In particular cases, retainer 30can be placed between portions of the two parts so that removal of oneof the parts from within the other is impeded or prevented. As shown inFIGS. 5 and 6, an example of such an implant is a multi-axial bone screwhaving a receiver member and an anchor member, and retainer 30 can beplaced in the receiver member and around a portion of the anchor memberso that the anchor member is held or retained in the receiver member.

Retainer 30 includes separate pieces 32, which in the illustratedembodiment are substantially identical and generally form part of acircle. A particular embodiment of piece 32 includes a central portion34, a first arm 36 and a second arm 38, and opposed substantially planarsurfaces 40 and 42. Surface 40 extends between arm 36 and centralportion 34, and surface 42 extends between arm 38 and central portion34. Arm 36 and central portion 34 are thus substantially contiguousalong surface 40, and arm 38 and central portion 34 are substantiallycontiguous along surface 42. Each arm 36, 38 is stepped from centralportion 34 in this embodiment, and arms 36 and 38 have respectiveinternal surfaces 44 and 46 that, in the illustrated embodiment, aresubstantially parallel to surfaces 40 and 42. Central portion 34 is thethickest portion, having a height H1 that is substantially the sum ofthe heights H2 and H3 of arms 36 and 38. In a particular embodiment,heights H2 and H3 are substantially equal, making height H1substantially twice the value of H2 or H3. Piece 32 has a width Wmeasured along the radius. In the illustrated embodiment, piece 32extends along an arc of more than 180 degrees from the end of arm 36 tothe end of arm 38, and in a particular embodiment that arc isapproximately 240 degrees.

As previously noted, the illustrated embodiment of retainer 30 includestwo substantially identical pieces 32. As seen in FIGS. 1 and 2, onepiece 32 is placed with respect to the other piece 32 so that theirrespective arms overlap. Thus, surface 44 of each piece 32 abuts atleast a portion of surface 46 of the other piece 32, and pieces 32 forma full circle. In the illustrated embodiment, when pieces 32 areabutting to form retainer 30, gaps 48 are present between centralportion 34 of each piece 32 and the other piece's arms. Gaps 48 mayallow for circumferential adjustment of the relative positions of pieces32, e.g. pivoting one piece 32 relative to the other piece 32 along thecircumference of each, and for collapsing of pieces 32 on themselves forpositioning with respect to another device, as further discussed below.Retainer 30, when assembled, provides for an aperture 50 defined bypieces 32.

In use, retainer 30 can be placed in or around parts of an orthopedicimplant so as to keep those parts together. As one example, amulti-axial bone implant 52 with which retainer 30 can be used is shownin FIGS. 4 and 5. Implant 52 includes a receiver member 54 having achannel 56 for an orthopedic elongated member (such as a spinal rod) andan anchor 58, such as a screw member with an enlarged head portion 60.Examples of implants with which retainer 30 can be used are shown inU.S. Pat. No. 6,280,442 and U.S. Pat. No. 6,485,491, which areincorporated herein by reference in their entireties. It will be seenthat receiver member 54 has a groove 62 proximate to a lower end ofreceiver member 54, which extends around the entire interior of receivermember 54. Groove 62 has a groove height that is approximately the sameas or somewhat larger than height H1 of pieces 32, and a groove widththat is slightly less than width W of pieces 32. In this illustratedembodiment, groove 62 is substantially circular in configuration,although it will be seen that groove 62 could have an oblong, oval,square, or other configuration.

In one embodiment, head 60 of anchor 58 is inserted into receiver member54 so that some or all of head 60 is substantially above groove 62.Retainer 30 is placed in groove 62 and around anchor 58 below head 60.Pieces 32 can be individually inserted into groove 62, or both pieces 32can be inserted substantially simultaneously, e.g. by placing pieces 32so that respective surfaces 44 and 46 abut, moving pieces 32 together sothat they do not form a circle, moving pieces 32 along anchor 58 and/orto a position adjacent groove 62, and spreading pieces 32 apart so thatthey enter respective parts of groove 62. Generally speaking, pieces 32of retainer 30 can be arranged with respect to each other as disclosedherein, e.g. so that a portion of at least one piece 32 overlaps atleast a portion of another piece 32, or so that both arms of each piece32 overlap respective arms of another piece 32, at the same time, priorto or after they are connected to implant 52 so that receiver member 54and anchor 58 are retained in a relative relationship. Thus, pieces 32may be seated in groove 62 so that at least a portion of the outer wallof pieces 32 contact receiver member 54. Aperture 50 formed by pieces 32is smaller than a minimum width or diameter of head 60, in theillustrated embodiment, so that head 60 is impeded or prevented frombeing pulled through pieces 32 and out of receiver member 54. Anelongated member, such as rod R, can be connected with the illustratedembodiment of implant 52, although other types of implants may not becapable of such connection to an elongated member.

Assembly of retainer 30 with an orthopedic implant, such as implant 52,may take place at or after manufacture of the individual parts of theimplant and retainer 30, and/or prior to or during a surgical procedure.If such assembly takes place prior to use in surgery, the assembledimplant and retainer combination can be moved to a surgical site andplaced as desired by the surgeon. Other procedures may be performed andother structure may be connected to the implant. For example, in a casewhere an implant such as implant 52 is used, the surgeon can insertimplant 52 (with retainer 30 retaining anchor 58 in receiver member 54)to a surgical site. Anchor 58 can be attached to bone, e.g. by screwinginto a vertebra via a screwdriver or other tool (not shown) insertedthrough receiver member 54 and into contact with head 60 of anchor 58.When anchor 58 is attached as desired, receiver member 54 ismulti-axially pivotable with respect to anchor 58. A rod or otherelongated member (not shown) can be inserted into channel 56 and lockedto receiver member 54, and receiver member 54 can be locked (with orwithout intermediate parts) with respect to anchor 58. Other devices,such as connectors, clamps, plates, additional rods, or other implants,can be connected to implant 52 or the rod it is attached to.Distraction, compression or rotation of vertebrae, placement of fusioncages or other devices, or other procedures can be performed before orafter placement of implant 52 or placement of a rod with respect toimplant 52. When all desired procedures have been completed, the surgeoncloses in a manner he or she may prefer.

Referring now generally to FIGS. 7-9, a retainer 130 composed of twopieces 132 is quite similar to retainer 30, described above. Pieces 132,are substantially identical and generally form part of a circle in theillustrated embodiment. Central portion 134 and arms 136 and 138 aresubstantially the same as central portion 34 and arms 36 and 38described above, with the exception of the end portions 137 and 139 ofarms 136 and 138. In the illustrated embodiment, end portions 137 and139 are bent, with respect to the rest of arms 136 and 138, generallytoward central portion 134. The terms “bend” and “bent” used hereinrefer to a non-coplanar or uneven shape or configuration, but not to aparticular method of obtaining such a shape or configuration. Whenpieces 132 are assembled into retainer 130, each piece's end portion 137is adjacent the other piece's end portion 139. This nested arrangementof bent end portions 137 and 139 may provide some resistance tocircumferential relative movement between pieces 132, where suchresistance is desired. The arrangement may also provide for easyrelative placement of pieces 132, as portions 137 and 139 may behavesimilarly to a ball-detent mechanism to indicate proper or preferredpositioning of pieces 132 with respect to each other. Further, bentportions 137 and 139 may act as springs, collapsing when retainer 130 isinserted into a groove (e.g. groove 62 described above), and providingfurther resistance to rotational or other movement of pieces 132relative to each other or to an implant to which retainer 30 isconnected. Thus, bent portions 137 and 139, when nested together, mayhave a height that is slightly greater than the height of groove 62, sothat groove 62 compresses or collapses portions 137 and 139 whenretainer 130 is inserted into groove 62.

In other embodiments, only one arm (e.g. arm 136) may have a bentportion (e.g. portion 137), so that bent portion 137 is adjacent anunbent arm 138. Alternatively, arm 136 of one piece 132 may have a bentportion 137, and arm 138 of the other piece 132 may have a bent portion139, so that one side of retainer 130 has bent portions 137 and 139facing each other, and another side of retainer 130 has unbent arms 136and 138 abutting each other. FIG. 9 shows an embodiment in which endportions 137 and 139 have two bends, making a first bent end portion 137a, 137 b and a second bend end portion 139 a, 139 b.

Turning now to FIGS. 10-11, there is shown an embodiment of retainer 230that is substantially identical in most respects to the embodiment ofretainer 30 shown in FIGS. 1-2. Retainer 230 includes separate pieces232, which in the illustrated embodiment are substantially identical andgenerally form part of a circle. As with the depicted embodiment ofretainer 30, the illustrated embodiment of retainer 230 includes acentral portion 234, a first arm 236 and a second arm 238, and opposedsubstantially planar surfaces 240 and 242. The main difference betweenretainer 230 and retainer 30 is in the relative thicknesses of arms 236and 238. Central portion 234 is the thickest portion, having a heightthat is substantially the sum of the heights of arms 236 and 238.Retainer 230 has arms 236 and 238 with heights that are not equal, withthe height of arm 236 being substantially greater than the height of arm238 in the illustrated embodiment. In one particular embodiment, theheight of arm 236 is approximately twice that of arm 238, and thus theheight of arm 236 is approximately two-thirds the height of centralportion 234, and the height of arm 238 is approximately one-third theheight of central portion 234. In other respects, retainer 230 issubstantially the same as retainer 30.

A further embodiment of retainer 330 is illustrated in FIGS. 12-13.Retainer 330 is similar to retainer 30 in many respects and can be usedfor the same purposes and in the same applications as retainer 30.Retainer 330 includes separate pieces 332, which in the illustratedembodiment are substantially identical and generally form part of acircle. A particular embodiment of piece 332 includes a central portion334, a first arm 336 and a second arm 338, and opposed substantiallyplanar surfaces 340 and 342. Surface 340 extends between arm 336 andcentral portion 334, and surface 342 extends between arm 338 and centralportion 334. Arm 336 and central portion 334 are thus substantiallycontiguous along surface 340, and arm 338 and central portion 334 aresubstantially contiguous along surface 342. Arms 336, 338 haverespective surfaces 344 and 346 that are sloped from central portion 334in this embodiment. Surface 344 meets but is non-planar with surface342, and surface 346 meets but is non-planar with surface 340. Centralportion 334 is the thickest portion, with arms 336 and 338 tapering torelatively thin ends 351 and 353, respectively. In a particularembodiment, the heights of ends 351 and 353 are substantially equal, andare at least slightly less than half of the height of central portion334. In that embodiment, when pieces 332 are overlapped to make retainer330 (FIG. 13), the overlapping parts of arms 336 and 338 areapproximately the same height as central portion 334. In other respects,retainer 330 is substantially the same as retainer 30.

Referring generally to FIGS. 14-15, there is shown an embodiment of aretainer 430 that is similar in most respects to retainer 30, and isused for the same purposes and in connection with the same types ofdevices. Retainer 430 includes separate pieces 432, which in theillustrated embodiment are substantially identical and generally formpart of a circle. A particular embodiment of piece 432 includes acentral portion 434, a first arm 436 and a second arm 438. In thisembodiment, a surface 440 that is substantially planar extends from arm436 through central portion 434 and over to arm 438. Arms 436 and 438and central portion 434 are thus substantially contiguous along surface440 in this embodiment. Each arm 436, 438 is stepped from centralportion 434 to the same side of central portion 434, so to speak,instead of to opposite sides of a central portion as in the illustratedembodiment of retainer 30. Arms 436 and 438 have respective internalsurfaces 444 and 446 that, in the illustrated embodiment, aresubstantially parallel to surface 440. Arms 436 and 438 may havethicknesses that are approximately equal in one embodiment. Centralportion 434 is the thickest portion, having a height that in aparticular embodiment is substantially twice the value of thethicknesses of arms 436 and 438. In other respects, retainer 430 issubstantially the same as retainer 30.

As previously noted, the illustrated embodiment of retainer 430 includestwo substantially identical pieces 432. As seen in FIG. 15, one piece432 is inverted with respect to the other piece 432, and the two piecesare placed with respect to each other so that their respective armsoverlap. Thus, the surfaces 444 of each piece 432 abut at least aportion of each other, the surfaces 446 of each piece 432 abut at leasta portion of each other, and pieces 432 form a full circle.

Referring now generally to FIGS. 16 and 17 there is shown a furtherembodiment of a retainer 530 having similarities to the illustratedembodiment of retainer 430, and which can be used for the same purposesand with similar devices to those with which other retainer embodimentsdisclosed herein are used.

Retainer 530 includes separate pieces 532, which in the illustratedembodiment are substantially identical and generally form part of acircle. A particular embodiment of piece 532 includes a central portion534, a first arm 536 and a second arm 538. Each of arms 536 and 538 andcentral portion 534 are substantially identically shaped and sized inthis illustrated embodiment. A first S-like bend 539 is between arm 536and central portion 534, and a second S-like bend 541 is between arm 538and central portion 534. Arms 536 and 538 and central portion 534 arethus wavy, having upper and lower surfaces that are contiguous from arm536, through S-bend 539, central portion 534 and S-bend 541, to arm 538.In other respects, retainer 530 is substantially the same as retainer430.

As previously noted, the illustrated embodiment of retainer 530 includestwo substantially identical pieces 532. As seen in FIG. 17, one piece532 is inverted with respect to the other piece 532, and the two piecesare placed with respect to each other so that their respective armsoverlap. Thus, arms 536 and 538 of a first piece 532 each overlap andabut the respective arms 536 and 538 of the other piece 532, and pieces532 form a full circle. Arms 536 and 538 are shown generally to the sameside of central portion 534 in this illustrated embodiment. That is,referring to the top of piece 532 as seen in FIG. 16 for convenience,there is an up-slope at 539 and 541 between central portion 534 and eachof arms 536 and 538. In other embodiments (e.g. retainer 530′ in FIGS.18-19) arms such as arms 536′ and 538′ may be on generally differentsides of a central portion such as central portion 534′. That is,referring to the top of piece 532′ as seen in FIG. 18 for convenience,there is an up-slope at 539 between central portion 534′ and arm 536′,and a down-slope 541′ between central portion 534′ and arm 538. Two suchpieces 532′ can be placed together to form retainer 530′, which in otherrespects is similar or identical to retainer 530 or other retainerembodiment disclosed herein.

FIGS. 20 and 21 show a further embodiment of a retainer 630 that isessentially identical to the illustrated embodiment of retainer 30,except that retainer 630 uses three substantially identical pieces 632.Pieces 632 are substantially the same as pieces 32, described above,having arms 636 and 638 that are substantially the same as arms 36 and38, and for brevity's sake that description is not repeated here.However, pieces 632 cover somewhat less of an arc than pieces 32 cover.In the illustrated embodiment, pieces 632 extend along an arc of morethan 120 degrees from the end of one arm 636 to the end of arm 638, andin a particular embodiment that arc is approximately 135 degrees ormore.

As previously noted, the illustrated embodiment of retainer 630 includessubstantially identical pieces 632. As with other embodiments, one piece632 is placed with respect to the other piece 632 so that theirrespective arms overlap. Thus, arm 636 of each piece 632 abuts at leasta portion of arm 638 of a neighboring piece 632, and pieces 632 form atleast substantially a full circle. In the illustrated embodiment, whenpieces 632 are abutting to form retainer 630, gaps 648 are presentbetween central portion 634 of each piece 632 and a neighboring piece'sarms. Gaps 648 may allow for circumferential adjustment of the relativepositions of pieces 632, e.g. pivoting one piece 632 relative to theother piece 632 along the circumference of each, or for collapsing ofpieces 632 for assembly with other device(s), substantially as describedabove. Retainer 630, when assembled, provides for an aperture 650defined by pieces 632.

FIGS. 22 and 23 show a further embodiment of a retainer 730 that isquite similar to other illustrated embodiments of a retainer. Retainer730 includes two substantially identical pieces 732. Pieces 732 eachhave a central portion 734 connected to arms 736 and 738, much asdescribed above with respect to piece 32. In the illustrated embodimentof piece 732, central portion 734 is substantially of the same thicknessas each arm 736 and 738, and is stepped from each arm 736 and 738. Thus,as seen in FIG. 22, as one moves from arm 736 to central portion 734,there is a step up, and as one moves from central portion to arm 738,there is another step up. Piece 732 may be thought of as the same aspiece 32, but having a central portion 734 with cut-outs on top andbottom, eliminating the common surfaces central portion 34 shares witharms 36 and 38 in the illustrated embodiment of piece 32.

As with other embodiments, one piece 732 is placed with respect to theother piece 732 so that at least one of their respective arms overlap toform retainer 730. Thus, in the illustrated embodiment arm 736 of eachpiece 732 abuts at least a portion of arm 738 of the other piece 732, sothat pieces 732 form at least substantially a full circle. When pieces732 are abutting or adjacent to form retainer 730, gaps 748 are presentbetween central portion 734 of each piece 732 and a neighboring piece'sarms. Gaps 748 may allow for circumferential adjustment of the relativepositions of pieces 732, e.g. pivoting one piece 732 relative to theother piece 732 along the circumference of each, or for collapsing ofpieces 732 for assembly with other device(s), substantially as describedabove. Retainer 730, when assembled, provides for an aperture 750defined by pieces 732.

Retainers as disclosed herein may be made out of stainless steel,titanium, certain hard plastics or ceramics, among other materials. Itwill be recognized that any sturdy biocompatible material may be used toconstruct the disclosed retainers.

Exemplary embodiments of retainers have been disclosed above. It will beseen that modifications may be made to those embodiments. For example,the inside edges of the illustrated embodiments of retainers (e.g. theedges adjacent opening 50 in retainer 30) are generally depicted assharp corners. In other embodiments, such inside edges of theconstituent pieces of the retainers may have curved (e.g. spherical),conical, sloped or other surfaces to accommodate pivoting of a bonescrew or other part. Similarly, surface 40 of retainer 30, or analogoussurfaces of other embodiments of retainers disclosed herein, could becurved or rounded, such that a cross section through an arm or centralportion of such a retainer would show an arced, part-circular or whollycircular shape.

Retainers as disclosed herein may be used with a number of differentapparatus for which it is desired to retain or hold one part within orwith respect to another. Such apparatus may include various embodimentsof bone screws, as discussed above, as well as orthopedic hooks, clamps,bolts, connectors, prostheses, fusion devices, and the like.

It is intended that various parts of the embodiments disclosed above canbe used with or incorporated into other embodiments. As one example, the“bent” ends shown in FIGS. 7-9 and described in the text may be usedwith other embodiments, such as the “same side” embodiment of FIGS.14-15. Further, the description above notes that in several embodimentsidentical pieces are used to make a particular retainer. It is intendedthat unlike pieces may be used to create a retainer. As one particularexample, a piece 32 could be used with a piece 132, a piece 232, orother pieces to create what could be called a hybrid retainer.

It will also be seen that the illustrated retainer embodiments generallyoverlap on two sides so that the retainer forms a complete circle. It ispossible to have two pieces (e.g. pieces 32) sized and configured sothat they need only overlap on one side, or potentially not overlap atall, and still operate together to retain one part within or withrespect to another. For example, in a construct such at that shown inFIGS. 5 and 6, the dimensions of pieces 32 can be chosen with respect tothe given dimensions of receiver member 54, head portion 60 and groove62 so that pieces 32 overlap on one side or not at all when placed ingroove 62, yet the diameter of the opening between pieces 32 is smallerthan the diameter of head portion 60. In such a situation, even thoughpieces 32 do not form an entire circle, or in cases in which pieces 32form an oblong or non-circular interior opening, they still perform as aretainer to hold head portion 60 in receiver member 54. Similarly, it isnot necessary to have the outer profile of retainer as disclosed hereinbe strictly circular. As long as an opening between its respectivepieces is smaller than a portion of an anchor, a retainer as disclosedabove may be oblong, oval, partially circular or otherwise configured.Thus, where a groove (such as groove 62) is non-circular, a retainerembodiment in that groove need not necessarily have a circular outerprofile.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly illustrated embodiments have been shown and described and that allchanges and modifications that come within the spirit of the disclosureare desired to be protected.

1. A retaining ring for use with orthopedic medical apparatus,comprising: a first arcuate piece having a central portion, a first arm,and a second arm; and a second arcuate piece having a central portion, afirst arm, and a second arm, said second arcuate piece beingnon-integral with said first arcuate piece; wherein said first andsecond pieces are arranged so that at least part of one of said arms ofsaid first element overlaps at least one of said arms of said secondelement.
 2. The apparatus of claim 1, wherein said first arm of saidfirst piece overlaps said second arm portion of said second piece, andsaid second arm of said first piece overlaps said first arm of saidsecond piece.
 3. The apparatus of claim 1, further comprising a thirdarcuate piece, said third piece having a central portion, a first armand a second arm.
 4. The apparatus of claim 3, wherein said first arm ofsaid first piece overlaps at least part of said first arm of said secondpiece, said second arm of said second piece overlaps at least part ofsaid first arm of said third piece, and said second arm of said thirdpiece overlaps at least part of said second arm of said first piece. 5.The apparatus of claim 1, wherein said first and second pieces aresubstantially identical.
 6. The apparatus of claim 1, wherein said armsof at least one of said pieces have a height that is substantiallyequal, and said central portion of said at least one of said pieces hasa height that is approximately twice said height of said arms.
 7. Theapparatus of claim 1, wherein said central portion of at least one ofsaid pieces has a first surface contiguous with said first arm of saidat least one of said pieces, and a second surface opposed to said firstsurface and contiguous with said second arm of said at least one of saidpieces.
 8. The apparatus of claim 1, wherein said central portion of atleast one of said pieces has a surface contiguous with said first armand said second arm of said at least one of said pieces.
 9. Theapparatus of claim 1, wherein said central portion of at least one ofsaid pieces includes a surface, and at least one of said arms of said atleast one of said pieces includes a portion that is non-coplanar withrespect to said surface.
 10. The apparatus of claim 9, wherein said atleast one of said arms has an end portion with at least one bend. 11.The apparatus of claim 9, wherein said at least one of said arms has anend portion with at least two bends.
 12. The apparatus of claim 9,wherein substantially all of said at least one of said arms is slopedwith respect to said surface.
 13. The apparatus of claim 1, wherein atleast one of said arms of said first piece nests inside at least one ofsaid arms of said second piece, said nesting providing at least one ofresistance to relative rotational movement between said pieces and anindication of proper relative positioning of said pieces.
 14. Theapparatus of claim 1, further comprising an anchor member having a head,said head having a diameter, wherein a distance between said first andsecond pieces is smaller than said diameter of said head.
 15. Theapparatus of claim 14, further comprising an elongated member connectedto said receiver member.
 16. An orthopedic medical apparatus,comprising: a receiver member having a lower opening and a groove aroundsaid lower opening; a first retaining piece having a central portion, afirst arm and a second arm; and a second retaining piece having acentral portion, a first arm and a second arm, said second retainingpiece being non-integral with said first retaining piece; wherein saidretaining pieces are each at least partially within said groove.
 17. Theapparatus of claim 16, wherein at least one of said arms of said firstretaining piece and at least one of said arms of said second retainingpiece at least partially overlap.
 18. The apparatus of claim 16, whereinsaid first arm of said first retaining piece overlaps at least part ofsaid first arm of said second retaining piece, and said second arm ofsaid first retaining piece overlaps at least part of said second arm ofsaid second retaining piece.
 19. The apparatus of claim 16, furthercomprising a third retaining piece, said third retaining piece having acentral portion, a first arm and a second arm.
 20. The apparatus ofclaim 19, wherein said first arm of said first retaining piece overlapsat least part of said first arm of said second retaining piece, saidsecond arm of said second retaining piece overlaps at least part of saidfirst arm of said third retaining piece, and said second arm of saidthird retaining piece overlaps at least part of said second arm of saidfirst retaining piece.
 21. The apparatus of claim 16, wherein said firstand second retaining pieces are substantially identical.
 22. Theapparatus of claim 16, wherein said arms of at least one of saidretaining pieces have a height that is substantially equal, and saidcentral portion of said at least one of said retaining pieces has aheight that is approximately twice said height of said arms.
 23. Theapparatus of claim 22, wherein said groove has a height, and said heightof said central portion is approximately equal to or less than saidheight of said groove.
 24. The apparatus of claim 16, wherein saidcentral portion of at least one of said retaining pieces has a firstsurface contiguous with said first arm of said at least one of saidretaining pieces, and a second surface opposed to said first surface andcontiguous with said second arm of said at least one of said retainingpieces.
 25. The apparatus of claim 16, wherein said central portion ofat least one of said retaining pieces has a surface contiguous with saidfirst arm and said second arm of said at least one of said retainingpieces.
 26. The apparatus of claim 16, wherein said central portion ofat least one of said retaining pieces includes a surface, and at leastone of said arms of said at least one of said retaining pieces includesa portion that is sloped with respect to said surface.
 27. The apparatusof claim 26, wherein said at least one of said arms has an end portionwith at least one bend.
 28. The apparatus of claim 26, wherein said atleast one of said arms has an end portion with at least two bends. 29.The apparatus of claim 26, wherein substantially all of said at leastone of said arms is sloped with respect to said surface.
 30. Theapparatus of claim 16, further comprising an anchor member having ahead, said head having a diameter, wherein a distance between said firstand second retaining pieces is smaller than said diameter of said head.31. The apparatus of claim 30, further comprising an elongated memberconnected to said receiver member.
 32. A method comprising: providing afirst arcuate retaining piece and a second arcuate retaining piece;arranging said first and second pieces so that a portion of at least oneof said pieces overlaps at least a portion of the other of said pieces;connecting said first and second pieces to an orthopedic medical devicehaving a first part and a second part, so that said first part and saidsecond part are retained in a relative relationship.
 33. The method ofclaim 32, wherein said arranging and said connecting step are performedat substantially the same time.
 34. The method of claim 32, wherein saidarranging step results in said first and second pieces overlapping attwo portions.
 35. The method of claim 32, wherein said first part ofsaid orthopedic medical device is a receiver member and said second partof said orthopedic medical device is a bone anchor having a head, andsaid connecting step includes connecting said pieces to said receivermember and around said bone anchor so that said bone anchor head cannotpass said pieces.
 36. The method of claim 32, wherein said orthopedicmedical device is an implant, and further comprising connecting anelongated member to said implant.